Combined steam reforming of methanol over Cu-Mn spinel oxide catalysts

Cu-Mn spinel oxide catalysts were synthesized by the combustion method, and their behavior in the combined steam reforming of methanol was examined. It was found that despite their low surface areas, these catalysts had comparable activity to that of a commercial Cu-Zn-Al catalyst for the production of H-2 via (combined) steam reforming of methanol. The fresh Cu-Mn catalysts were composed of the spinel phase Cu1.5Mn1.5O4, as well as Mn2O3 and CuO, depending on the Cu/Mn ratio, and were reduced to Cuo and MnO under reaction conditions. XPS analysis revealed the presence of two different oxidation states in both copper (Cu2+ and Cu+) and manganese (Mn4+ and Mn3+) in fresh catalysts and decomposition of the spinel in used catalysts. The optimal catalyst was prepared with a Cu/(Cu + Mn) ratio of 0.30. At a higher copper content (x = 0.40, 0.50), the excess copper was not incorporated into the spinel but instead was present as a separate CuO phase. A transient reduction/oxidation behavior was noted in the course of successive TPR/TPO cycles, as the efficiency of spinel reformation during oxidation of the reduced catalyst gradually diminished. The amount of CO produced from reforming was well below water-gas shift equilibrium, indicating that CO2 was the primary product, whereas CO was produced by the reverse water-gas shift reaction. TPO measurements after methanol-reforming runs indicated only minimal carbon deposition. (c) 2007 Elsevier Inc. All rights reserved.